Vinegar removes rust directly. Might take a few hours. Get a gallon of vinegar and put the pan in a container just large enough to hold it, then pour the vinegar in. Keep an eye on it, it will start bubbling. Use a toothbrush to test how well it is doing. When the rust is turned dark, use plain water and a plastic scrubby to get the black all off, immediately oil it with the highest smoke point oil you can. Wipe off as much oil as possible. Put it in a cold oven. Set it to 500 and let it bake for an hour at 500. Turn off the oven and let it cool on its own. (You can do that on a grill too, if the smoke bothers you.) I use Chosen brand 500 degree spray olive oil. Weber makes a high temp grill oil too. You can do that whole heating process 3 times or more until it is black enough for you. Make sure to hit all surfaces each time to make it fully seasoned and ward off any more rust. Keep it away from soap in the future. All it takes is water and a scraper if stuff sticks. Most sticking is caused by putting food in before the pan is heated, and/or letting food sit and dry in it after using it. My dutch oven was treated like this over 10 years ago and is still fine.